* [fix] the risk for function exit() when open pthread support.
* [update] modify annotation from "user data" to "pthread_data".

Signed-off-by: NJianhui Zhao <zhaojh329@gmail.com>

* [kernel] update comments for rt_thread_suspend

When we create thread A by rt_thread_init but do
    not init the thread object,and then create thread
    B in the thread A,it maybe crash.